Source : Webster's Revised Unabridged Dictionary (1913)

Nosebag \Nose"bag`\, n.
   A bag in which feed for a horse, ox, or the like, may be
   fastened under the nose by a string passing over the head.

Source : WordNet®

nosebag
     n : a canvas bag that is used to feed an animal (such as a
         horse); covers the muzzle and fastens at the top of the
         head [syn: {feedbag}]